Comparative evaluation of schistocyte counting by an automated method and by microscopic determination

Schistocytes are circulating RBC fragments. The morphologic identification of schistocytes is difficult because the shapes to which they correspond are still under discussion. Automated hematology systems permit the possibility of direct measurement of RBC fragments. We compared schistocyte counts performed by different biologists and technicians with the automated counts by the ADVIA 120 (Bayer Health Care, Tarrytown, NY). The agreement between the ADVIA 120 and the average of the observers gives a correlation coefficient of 0.7274 (95% confidence interval, 0.6285-0.8019). The ADVIA 120 has a tendency to overestimate the count (average, +0.445%). No false-negative case was recorded. The maximum sensitivity (detection of 100% of samples with schistocytes) of the analyzer was determined at a threshold value of 0.25%, but the specificity was low (20%). Therefore, a blood smear examination remains necessary to confirm schistocyte presence. However, the clinical features correlated particularly with negative automated RBC fragments, and the high negative predictive value of RBC fragments ruled out thrombotic events (macroangiopathies or microangiopathies).